Periodic Reporting for period 1 - TERRAMETA (TERahertz ReconfigurAble METAsurfaces for ultra-high rate wireless communications)
Reporting period: 2023-01-01 to 2024-06-30
The sixth generation of mobile communications, planned around 2030, is expected to support innovative applications with requirements not met with today’s technologies, such as massive-scale communications (within IoT), the Internet of senses, holographic communications, massive digital twinning and Extreme Reality, full autonomous driving and flying networks, considering use cases in smart cities, smart home and factories (e.g. ultra-high precision 3D positioning). With the emergence of viable THz communications systems on the horizon, new contributions in THz communication and networking are crucial for establishing the 6G technology roadmap and getting closer to industrial uptake.
The TERRAMETA project aims to investigate ground-breaking technologies for the sixth generation (6G) of mobile communications and demonstrate the feasibility of ultra-high data rate wireless networks leveraging on THz Reconfigurable Intelligent Surfaces (RISs). Novel high-performance hardware will be developed, including low power consumption THz wideband switches, THz RIS, and THz transmitter/receiver. Then, advanced network analysis/optimization techniques will be investigated using these real THz components. The proposed TERRAMETA THz network will be driven by 6G usage scenario requirements and indoor, outdoor, and indoor-to-outdoor scenarios to be demonstrated in a real factory setting and telecom testing field. It is expected that the outcome of this project will significantly progress innovations for across the 6G technology and systems.
The TERRAMETA project aims to investigate ground-breaking technologies for the sixth generation (6G) of mobile communications and demonstrate the feasibility of ultra-high data rate wireless networks leveraging on THz Reconfigurable Intelligent Surfaces (RISs). Novel high-performance hardware will be developed, including low power consumption THz wideband switches, THz RIS, and THz transmitter/receiver. Then, advanced network analysis/optimization techniques will be investigated using these real THz components. The proposed TERRAMETA THz network will be driven by 6G usage scenario requirements and indoor, outdoor, and indoor-to-outdoor scenarios to be demonstrated in a real factory setting and telecom testing field. It is expected that the outcome of this project will significantly progress innovations for across the 6G technology and systems.
Considerable hardware developments have been made in WP3/WP4 along the three main lines defined in section 1.1 of the DoA: 1) novel RF switch technology assessment, 2) high power THz transmitter, and 3) electrically large Reconfigurable Intelligent Surface (RIS) design.
Switch level reconfigurable technologies being investigated at D-band (140 GHz):
i) Memristors
The work has been focused on the optimization of the structure and active layer of the memristor devices for the target requirements of the project. There was a patent application submitted in M12 (Application in Portugal) which protects the concept of using memristors for controlling unit-cells from transmit and reflect array antennas.
ii) Gallium Nitride (GaN)
The evaluation of the CEA GaN-on-Silicon technology for RF switch application has been approached with a design-of-experiment technique to implement a switch specific layout of test. RF characterization at lower frequencies has been completed in the first quarter of 2024. Results show the feasibility of this technology for high-quality switches capable of a unprecedent power-handling.
iii) Phase Change Materials (PCM)
Although not initially planned, a PCM based RF switch has been identified in Task 3.1 as a relevant option (described in D3.1). The switch has been experimentally characterized and integrated into a T-RIS unit cell design. A prototype fabrication (passive) considering the innovative on-glass packaging with TGV (through glass vias) is planned in Year 2. There was a patent application in year 1 (Application in France) protecting the concept of a RF switch based on a phase change material, as well as a unit cell design using this switch.
iv) Microfluidics
Several conductive liquid materials and microfluidic structures have been fabricated and tested. A RIS prototype with 16 independently actuated sub-array lines has been manufactured and its radiation pattern has been experimentally measured. This is arguably a pioneering result for its implementation in the form of RIS.
v) Schottky diodes
Although not initially planned, a Schottky diode-based RF switch from ACST’s portfolio has been identified in Task 3.1 as a relevant option. The switch will be experimentally characterized and integrated into R-RIS unit cell designs.
v) RF-switches based on GlobalFoundries® 45 nm RFSOI (GF 45)
The possibility to use the GF 45 process for the implementation of an innovative unit cell for D-band T-RIS has been investigated. A unit cell concept has been developed and the layout of a RFIC integrating several unit cells is being designed. There was a patent application in year 1 (Application in France) protecting the concept of a RF switch based on a CMOS process.
High power THz transmitter and receiver development
A high-power THz transmitter with ASK modulation has been designed using an amplitude modulator based on Schottky-diodes. Full-wave analysis predicts an unprecedent level of modulated power at 300 GHz.
Electrically large RIS design
A set of passive unit cells have been developed at 300 GHz for implementing the same R-RIS design with different phase quantization steps (1, 2 and 3 bits).
A D-band proof-of-concept of a 1-bit wideband RIS comprising planar tightly coupled dipoles was designed and manufactured. In this initial result fixed connections were used instead of real RF switches.
An innovative RIS technology has been developed based on the use of two interconnected T-RISs with 4-bits of phase resolution. This device is an innovative sub-THz repeater. A prototype has been designed and fabricated.
Four T-RIS prototypes based on an innovative glass-packaging technology with TGV have been developed. There was a patent application in year 2 (Application in France) protecting the concept of T-RIS based on PCM switches and corresponding manufacturing process.
Considerable progress towards the development of signal processing techniques for THz communications, localisation, and sensing with various forms of reconfigurable metasurfaces have been made as follows:
Measurement Campaign: Characterisation of the channel and the impact of reflective RIS and transmissive RIS using a 300 GHz channel sounder.
RIS-parametrised channel modelling and unit-cell modelling:
• A novel multi-user near-field channel model with holographic MIMO transceivers (e.g. metasurface-based antenna panels) and triple polarisation using the dyadic Green’s function has been developed.
Channel Estimation Algorithms:
• A time-domain channel estimation approach has been developed for umMIMO THz systems considering a spatial representation of the wideband channel and the beam-squint effect.
Beamforming Codebooks:
• A near-field dynamic codebook for directional beamforming has been investigated and implemented for a tracking scenario considering metasurface-based transceivers.
• A low-complexity neural-network-based beam training for THz beamforming has been studied considering an umMIMO system operating in the far-field,. Hierarchical codebook search assisted by a neural network to establish the relationship between the codewords in the angle domain to speed up the beam search was designed.
Beamforming Strategies:
• An optimal design of RISs to increase the rank of the channel matrix in umMIMO systems was proposed.
• A multi-user downlink beamforming scheme with leaky waveguide antennas for wideband THz systems, exploiting the THz rainbow effect, was devised [GSR24].
Localisation and Sensing:
• Proposed a RIS-enabled and access-point-free simultaneous radio localization and mapping method.
• Evaluated a joint 3D user and 6D hybrid RIS localization.
• Proposed a method based on full-duplex metasurface-based transceivers for integrated sensing and communication.
Switch level reconfigurable technologies being investigated at D-band (140 GHz):
i) Memristors
The work has been focused on the optimization of the structure and active layer of the memristor devices for the target requirements of the project. There was a patent application submitted in M12 (Application in Portugal) which protects the concept of using memristors for controlling unit-cells from transmit and reflect array antennas.
ii) Gallium Nitride (GaN)
The evaluation of the CEA GaN-on-Silicon technology for RF switch application has been approached with a design-of-experiment technique to implement a switch specific layout of test. RF characterization at lower frequencies has been completed in the first quarter of 2024. Results show the feasibility of this technology for high-quality switches capable of a unprecedent power-handling.
iii) Phase Change Materials (PCM)
Although not initially planned, a PCM based RF switch has been identified in Task 3.1 as a relevant option (described in D3.1). The switch has been experimentally characterized and integrated into a T-RIS unit cell design. A prototype fabrication (passive) considering the innovative on-glass packaging with TGV (through glass vias) is planned in Year 2. There was a patent application in year 1 (Application in France) protecting the concept of a RF switch based on a phase change material, as well as a unit cell design using this switch.
iv) Microfluidics
Several conductive liquid materials and microfluidic structures have been fabricated and tested. A RIS prototype with 16 independently actuated sub-array lines has been manufactured and its radiation pattern has been experimentally measured. This is arguably a pioneering result for its implementation in the form of RIS.
v) Schottky diodes
Although not initially planned, a Schottky diode-based RF switch from ACST’s portfolio has been identified in Task 3.1 as a relevant option. The switch will be experimentally characterized and integrated into R-RIS unit cell designs.
v) RF-switches based on GlobalFoundries® 45 nm RFSOI (GF 45)
The possibility to use the GF 45 process for the implementation of an innovative unit cell for D-band T-RIS has been investigated. A unit cell concept has been developed and the layout of a RFIC integrating several unit cells is being designed. There was a patent application in year 1 (Application in France) protecting the concept of a RF switch based on a CMOS process.
High power THz transmitter and receiver development
A high-power THz transmitter with ASK modulation has been designed using an amplitude modulator based on Schottky-diodes. Full-wave analysis predicts an unprecedent level of modulated power at 300 GHz.
Electrically large RIS design
A set of passive unit cells have been developed at 300 GHz for implementing the same R-RIS design with different phase quantization steps (1, 2 and 3 bits).
A D-band proof-of-concept of a 1-bit wideband RIS comprising planar tightly coupled dipoles was designed and manufactured. In this initial result fixed connections were used instead of real RF switches.
An innovative RIS technology has been developed based on the use of two interconnected T-RISs with 4-bits of phase resolution. This device is an innovative sub-THz repeater. A prototype has been designed and fabricated.
Four T-RIS prototypes based on an innovative glass-packaging technology with TGV have been developed. There was a patent application in year 2 (Application in France) protecting the concept of T-RIS based on PCM switches and corresponding manufacturing process.
Considerable progress towards the development of signal processing techniques for THz communications, localisation, and sensing with various forms of reconfigurable metasurfaces have been made as follows:
Measurement Campaign: Characterisation of the channel and the impact of reflective RIS and transmissive RIS using a 300 GHz channel sounder.
RIS-parametrised channel modelling and unit-cell modelling:
• A novel multi-user near-field channel model with holographic MIMO transceivers (e.g. metasurface-based antenna panels) and triple polarisation using the dyadic Green’s function has been developed.
Channel Estimation Algorithms:
• A time-domain channel estimation approach has been developed for umMIMO THz systems considering a spatial representation of the wideband channel and the beam-squint effect.
Beamforming Codebooks:
• A near-field dynamic codebook for directional beamforming has been investigated and implemented for a tracking scenario considering metasurface-based transceivers.
• A low-complexity neural-network-based beam training for THz beamforming has been studied considering an umMIMO system operating in the far-field,. Hierarchical codebook search assisted by a neural network to establish the relationship between the codewords in the angle domain to speed up the beam search was designed.
Beamforming Strategies:
• An optimal design of RISs to increase the rank of the channel matrix in umMIMO systems was proposed.
• A multi-user downlink beamforming scheme with leaky waveguide antennas for wideband THz systems, exploiting the THz rainbow effect, was devised [GSR24].
Localisation and Sensing:
• Proposed a RIS-enabled and access-point-free simultaneous radio localization and mapping method.
• Evaluated a joint 3D user and 6D hybrid RIS localization.
• Proposed a method based on full-duplex metasurface-based transceivers for integrated sensing and communication.